more displacement woes

[tom182]

Hi all,
I'm midway through this aeriel pic of a development and I am getting strange results with the displacement on my grass,
The first pic is with displacement (2D mapping) and you can see a dark region(s) on the grass, second pic is with no displacement. The mesh (prior to adding the displ modifer is simple and clean- i.e spline extruded),



any ideas,
Thanks,
Tom

[instinct]

Re: more displacement woes

(prior to adding the displ modifer is simple and clean- i.e spline extruded)

You might wanna show a wire to clarify, but "spline extruded" and "clean mesh" dont go well together :P

Even tho the edges are hidden, there is triangulation done, that often leads to long stretched triangles...and those cause trouble with displacement. You might wanna try converting to editable poly and manually add proper subdivision.

Thorsten

[Morbid Angel]

did you read my topology thread in tutorials section?

[tom182]

hmm,
@ instinct, do you mean that if I create a rectangle, convert to editable spline and add extrude that it wont give me a clean mesh, i would have thought it would. Yeah from thre pic you can see the triangulation, you suggest I convert to edit poly and add a subdivide modifier?

@morbid, I did read it and saw it soon after you posted it, I thought that you were addressing the problems associated with a) splines from a CAD package, b) boolean issues. Initially I didnt think that creating such a mesh would cause the issues you mention, obviously it does (
I just selected the top Poygon of the extrusion and sliced it up, that seemed to do the trick- one or two minor issues around the curves but hardly noticable, is this the logical ay to fix it?

If anyone has a quick solution the little $%$^$% of a scene is here http://www.coastal-cottage.com/rende...splacement.zip

thanks guys
Tom

[DaForce]

I would suggest you try the following (might work ok)

Lay a plane over the spline so that it just fits around it, and increase the segments so to maybe 4000 or so.. so that you get alot of nice even squares.
Then remove all mods from the spline so its just a spline then draw a spline rectangle around the original spline making sure it bigger then the plane. Then attach the original spline to the rectangle spline and extrude it so that you get a solid mesh with a hole where the displament should be.

Then move the new mesh down abit and run a boolean operation to remove the mesh from teh plan to leave a nice divided plan where the displacement should be. Ideally use powerbooleans or max8's boolean extension to make things as clean as possible.

Then uvw and displace as needed.

Thats basically going to be a neater version of what you are doing with the slicing/cutting, and this will only take a minute or so.

[Dynedain]

.... run a boolean operation to remove the mesh from teh plan to leave a nice divided plan...

BOOLEANS BAAAD!

A better solution would be to make a nicely subdivided plane and a cleaned-up version of your spline without modifiers (just like DaForce started with). Then, instead of adding another spline and doing extrudes and booleans, simply use the Shape Merge tool (compound objects) to "cookie-cutter" the spline out of the plane. The result will be a nicely subdivided grid in the shape of the spline. Collapse this to an editable mesh or poly, add UVW mapping and displacement.

Faster and cleaner than going the boolean route.

[DaForce]

lol

yeah i thought of that but i thought they would give basically identical results.... *shrugs*

After playing around with it, it seems Boolean didnt work the way i expected... i was after similar results to what Dynedain said but it doesnt seem to do that. but Dynedain's way is by far the better option.

Infact the end result was exactly what i was after with my suggestion.

[stephan_MA]

how did you map the grass? planar or cube? try cube, worked for me.

[tom182]

well its gone from bad to worse, having sliced up the top poly of the extrusion (which then gave a decent displacement) I have run into memory allocation issues, seems the disp is causing it. This is more serious as Max bombs out of the render.
The scene renders out fine with disp turned off in the globals option, but the grass doesnt look as good, solution: render all scene with no displacement, then render out seperate objects with disp added to them and comp in PS.
Mapping was planar, will try box but I kknow I will have the memory problem, (Dual Xeon 2.66, 2GB Ram)
Any tips on memory allocation when displacement is the culprit? Ohh I think a Hardware upgrade could be on the cards...thats another headache waiting to happen

cheers,
Tom

[stephan_MA]

how did you map the grass? planar or cube? try cube, worked for me.

[Dynedain]

well its gone from bad to worse, having sliced up the top poly of the extrusion (which then gave a decent displacement)...

Try it the way I suggested instead of the extrusion method.

[Sawyer]

I may be missing the point here but do you need displacement? If you have a bird eye view like this can't you fake it with bump? (or render antother scene with just displacement grass and use that as a texture in the building scene?)

[tom182]

If you have a bird eye view like this can't you fake it with bump?

I know what you mean but the Birds eye view is the first in a series of images needed, the rest are all eye (or there abouts) level of the development where displ'ment is needed. For the aerial shot I can achive the same result with bump and some tweaking in PS but considering the other images needed I would like to get the displacement sortyed so no matter what camera location I was at it would render out as I intended, paths, grassv erges are all at different z locations so turning displ off would cause other slowdowns in the workflow, (e.g moving them in the z so say the grass is not hiddden under the path)

@Dynedain, is that akin to projecting the spline onto the plane?

Cheers,
Tom

ps I posted a eye level view over in he image uploads section

[natty]

Cut a nicely subdivided plane into the space,,, should solve it.

[Dynedain]

Dynedain, is that akin to projecting the spline onto the plane?

Yes, but no extrusion is involved, you're more likely to have clean geomtery with topology suitable for displacement.